Creating a functioning valve gear in SOLIDWORKS is no simple task, particularly when precision is crucial to ensuring performance and accuracy. In this post, we’ll walk through validating the length of linkages using a skeleton sketch in SOLIDWORKS—a critical phase in building a fully functioning system.
Achieving Perfection with Research
The journey begins with some initial research and analysis of videos from reliable sources such as the Chesapeake and Ohio Railway Historical Society and an expert known as the eccentric engineer. These resources were pivotal in understanding the linkage function and the importance of their relative positions. Watching the eccentric engineer explain the process using SolidWorks made the task significantly more manageable.
Crafting the Skeleton Sketch
To commence the validation process, I created a skeleton sketch depicting the system’s forward-most and rear-most positions, along with the neutral position of the radius rod. This sketch ensures each segment is in alignment, replicating the model’s precise positioning in its actual state.
Cranking Up the Precision
Positioning the eccentric crank correctly is crucial. The design allows some flexibility; however, critical restrictions apply to ensure accuracy: the eccentric crank and rod must be appropriately angled and dimensioned. This alignment guarantees that the joint with the expansion link maintains the same XY position across all movements.
Understanding Valve Positioning: Lap and Lead
To delve deeper, we explore the correlation between lap and lead—terms defining valve positioning. Lap refers to the overlap when the valve piston is centered, while lead denotes the gap at the steam admission intake during full extension of the wheels. For this project, the lap measures 1.25 millimeters, and lead is about 0.49 millimeters. A comparative analysis with “The Big Boy” shows compatibility in the scale-specific measurements.
Fine-Tuning the Linkages
After compiling all dimensional data, adjustments were made in the assembly regarding the eccentric crank’s angle and lengths of both the eccentric rod and union link. This setup adjustment helps achieve a balanced movement, facilitating functionality at both neutral and full throttle positions.
Ensuring Consistent Valve Movement
Maintaining even valve movement at varying power settings is imperative. This required adding the forward and rearward swings of the expansion links into the skeleton sketch. Doing so allowed for simulating the operation of the radius rod and eccentric components. This simulation aids in determining the length of supporting elements like the lifting link, defined at 15 millimeters, and the lifting arm, at 18 millimeters.
Finalizing the Support
Lastly, the model includes a support beam, positioned accurately by referencing the skeleton sketch’s pivotal points. Ensuring that each dimension aligns flawlessly with empirical data guarantees that every linkage in the chain operates seamlessly.
More in this Locomotive Webinar Recap
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- Designing a 3D-Printed Steam Engine You Can Power With Compressed Air (Big Boy Inspiration)
- Designing Working Walschaerts Valve Gear in SOLIDWORKS: Validating Link Lengths, Lap & Lead
- Choosing FDM vs SLA for a 3D Printed Model: Stand Design, Part Planning, and Hardware Prep
- Crafting a G-Scale Replica: Designing the Iconic Big Boy Locomotive
- Designing and Testing Linkages in SOLIDWORKS: Clearances, Mates, and 3D-Printed Fit Checks
- Assembling a 3D-Printed Steam Engine Valve Gear: Fits, Clearances, and Iteration
- Why My 3D-Printed Steam Locomotive Kept Stalling (And How Quartering Fixed It)
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